Prions and viroids are two types of infectious agents that are even simpler than viruses. They were discovered relatively recently and have challenged the traditional concept of infectious agents. Prions are infectious proteins that contain no nucleic acids, while viroids are small, circular, single-stranded RNA molecules that do not code for any proteins. Both cause serious diseases in animals and plants.
Definition
Prions: Prions are infectious protein particles, smaller than viruses, that contain no nucleic acids (neither DNA nor RNA).
Viroids: Viroids are pathogens that consist of a short, circular, single-stranded RNA without a protein coat or envelope.
Prions = infectious proteins without nucleic acids.
Viroids = infectious RNA molecules without a protein coat.
Core Concept
The idea of an infectious agent that did not use nucleic acids and proteins together was considered impossible.
Pioneering work by Nobel Prize-winning biologist Stanley Prusiner has convinced the scientific community that prions exist.
Prions are infectious protein particles.
Viroids are infectious RNA molecules.
Both are smaller and simpler than viruses.
Both cause serious diseases.
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